1. Field of the Invention
The present invention relates to an image correcting method. The image correcting method can be used in, for example, a pattern inspection apparatus for inspecting the presence/absence of a defect of a micropattern image formed on a workpiece being tested such as a reticle used in, for example, manufacturing of an LSI.
2. Description of the Related Art
In general, since a lot of cost is required to manufacture an LSI, an increase in yield is inevitably sought. As one factor which decreases a yield, a pattern defect of a reticle used when a micropatterning image is exposed and transferred on a semiconductor wafer by a lithography technique is known. In recent years, with a miniaturization of LSI pattern size, the minimum size of a defect to be detected is also miniaturized. For this reason, a higher precision of a pattern inspection apparatus for inspecting a defect of a reticle is required.
Methods of inspecting the presence/absence of a pattern defect are roughly classified into a method of comparing a die with a die (Die-to-Die comparison) and a method of comparing a die with a database (Die-to-Database comparison). The Die-to-Die comparison (DD comparison) is a method of comparing two dies on a reticle to detect a defect. The Die-to-Database comparison (DB comparison) is a method of comparing a die and a database generated from CAD data for LSI design to detect a defect.
With micropatterning on a reticle, defects such as a pixel positioning error between images to be compared with each other, expansion and contraction and distortion of an image, defects which are small enough to be buried in sensing noise, must be detected. Even in the DD comparison or the DB comparison, alignment and image correction in a sub-pixel unit is very important in a pre-stage executing comparison and inspection of an inspection reference pattern image and a pattern image under test.
Therefore, in the conventional pre-stage in which two images, i.e., an inspection reference pattern image and a pattern image under test are inspected by comparison, after alignment in units of sub-pixels based on bicubic interpolation is performed, a correction of expansion and contraction of an image (see, for example, Japanese Patent Application Laid-Open No. 2000-241136), a distortion correction of an image, a resizing correction, a noise averaging process, and the like are sequentially performed. However, a repetition of these corrections generates an accumulative error and serves as a main factor of deteriorating an image. Furthermore, setting of appropriate values a large number of parameters require for the respective corrections and setting of an appropriate order of the respective corrections are disadvantageously difficult.